A position of a person or object may be determined using a global positioning system (GPS) receiver, for example. However, to use a GPS receiver, a GPS antenna coupled to the GPS receiver needs a line of sight to GPS satellites. For increased accuracy, the number of GPS satellites having a line of sight to the GPS antenna increases. In other words, position determining using a GPS receiver may not work indoors, for example, or other location where the GPS antenna does not have a line of sight to the sky.
In such GPS denied locations, a person or object may be tracked using an inertial measurement unit (IMU). An inertial measurement unit may cooperate with an accelerometer to calculate displacement, for example. More particularly, a determined acceleration may be first integrated over a time period to determine a velocity. The velocity may be integrated over the time period to determine the displacement. In other words, a double integration is performed on the acceleration to arrive at the displacement.
Velocity drift due to accumulation of errors or noise may contribute to inaccuracies in determining the displacement over the time period. Additionally, gyroscope drift and bias in systems that include a gyroscope, for direction, for example, may also contribute to displacement inaccuracies over the time period. Moreover, performing the double integration of the determined acceleration over the time period, especially if the time period is relatively long or includes a relatively large amount of data samples from the accelerometer, typically introduces a relatively large error over the time period.
When the IMU is measured via a mobile device carried by a user, the process for location determining is known as pedestrian dead reckoning (PDR). In essence, the mobile device connects the dots from the last known position to attempt to determine the current location.